Responding to an appeal for more forces in Iraq to help manage a rising number of detainees, the Pentagon is dispatching an additional 700 troops from the 82nd Airborne Division, defense officials said yesterday.

The previously unscheduled deployment is intended specifically to bolster prison operations, the officials said. It is not part of a temporary increase in U.S. troop levels in Iraq that commanders have said is likely to enhance security for a planned constitutional referendum in October and governmental elections in December.

"The basic fact driving this deployment is the steady rise in the prison population," said Lt. Col. Barry Venable, a Pentagon spokesman. "There need to be some additional resources devoted to this."

The number of prisoners held in U.S. military detention centers in Iraq has more than doubled since the autumn, climbing from 5,400 in September to more than 10,800 now, according to the latest Pentagon figures. The surge has filled existing prisons to capacity and prompted commanders to embark on an unanticipated prison expansion plan.

Military officials have attributed the influx of detainees to intensified counterinsurgency operations by Iraqi as well as U.S. forces. But the burgeoning prison population also appears to reflect the persistence of the insurgency itself.

A formal request for more security forces came in May, officials said, and approval was granted last month. An announcement by the 82nd Airborne Division's headquarters at Fort Bragg, N.C., on Monday saying that the 1st battalion, 504th Parachute Infantry Regiment, will be going to Iraq contained no information about the unit's mission.

Pentagon officials said the unit will not necessarily provide prison guards but rather engage in a number of detention-related operations, such as securing the area around a prison compound or transporting detainees from one prison to another.

"They're going to assist however they're needed," Venable said. "But it's best to think of them as a security force, not as prison guards, although some things they might do could bring them into proximity with prisoners."

Crowded conditions at the U.S.-run prison camps and what commanders describe as an increasingly hard-core inmate population have produced a combustible mix, confronting U.S. forces with a growing risk of prison violence. Camp Bucca, a sprawling detention facility in the southern Iraqi desert near the Kuwaiti border where the majority of prisoners are held, experienced two large riots earlier this year.

The danger of outside attack also remains a concern. Last spring, U.S. forces repelled a significant assault by insurgents on Abu Ghraib prison, the U.S. military's primary interrogation center and the site of highly publicized cases of detainee abuse.

The U.S. military runs three main detention centers in Iraq: Camp Bucca in the south and Abu Ghraib and Camp Cropper in the Baghdad area. But anticipating a continued influx of detainees, a fourth prison, called Fort Suse, is being built on the site of a Russian-built former Iraqi military barracks near the northern city of Sulaymaniyah.

Defense Secretary Donald H. Rumsfeld, during a visit to Iraq last month, expressed interest in handing responsibility for detainees to Iraqi authorities "as soon as is feasible." But no date has been set for such a transfer.